1. Field of the Invention
The present invention relates generally to a communication system, and in particular, to a method for transmitting/receiving data in a communication system providing Multicast and Broadcast Service (MBS).
2. Description of the Related Art
In the next generation communication system, active research is being conducted to provide users with services varying in Quality-of-Service (QoS) and at a high data rate. Particularly, in the current next generation communication system, studies are being carried out to support high-speed services capable of guaranteeing mobility and a QoS in a Broadband Wireless Access (BWA) communication system such as a wireless Local Area Network (LAN) communication system and a wireless Metropolitan Area Network (MAN) communication system. The Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system is a typical BWA, LAN and MAN communication system.
The IEEE 802.16 communication system employs an Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme to support a broadband transmission network for physical channels of the wireless MAN system. The IEEE 802.16 communication system currently takes into account not only fixed elements of a system but also mobile a subscriber stations (SS). An SS having both fixed elements and mobile elements will be referred to as a mobile station (MS).
The BWA communication system provides user with high-speed multimedia communication service, for example, MBS, beyond the voice and packet data communication services provided in the existing communication system. That is, in a communication system providing MBS, a transmitter, for example, a base station (BS), provides broadcast contents to a plurality of receivers, for example, MSs, using a multicast scheme. The multicast scheme refers to a transmission scheme in which one transmitter transmits transmission data to a plurality of receivers. The communication system providing MBS divides its full broadcast service area into a plurality of service areas, and in each of the divided service areas, one or more transmitters transmit MBS data to all receivers located in their service area using the multicast scheme. The receivers located in each service area simultaneously receive the MBS data from their transmitter(s). In the communication system providing a MBS, one transmitter may manage more than one service areas and simultaneously provide the MBS to receivers located in the multiply service areas.
In the communication system providing the MBS, particularly in the IEEE 802.16 communication system, a transmitter transmits MBS data to receivers at the same frame number and the same MBS symbol position at the same time using the same coding scheme. In order to allow a receiver located in a boundary area of each service area to obtain a macro diversity effect through radio frequency combining, the transmitter should define an MBS field (or MBS zone) in a downlink frame and transmit the MBS data through the MBS field. The receiver receives an MBS-MAP message including information on an MBS field that it should receive in the downlink frame, to detect the MBS field, thereby receiving the MBS data transmitted through the MBS field. Herein, the MAP message transmitting downlink resource allocation information is referred to as a downlink-MAP (DL-MAP) message, and the MAP message transmitting uplink resource allocation information is referred to as an uplink-MAP (UL-MAP) message.
If the transmitter transmits downlink resource allocation information and uplink resource allocation information through the DL-MAP message and the UL-MAP message in this way, the receivers decode the DL-MAP message and ILL-MAP message transmitted by the transmitter to detect the allocation position of resources allocated thereto and the control information of the data they should receive. The MSs can transmit/receive data through the downlink and the uplink by detecting the resource allocation position and control information.
FIG. 1 is a diagram illustrating a structure of a downlink frame in a general communication system providing MBS. In FIG. 1, a downlink frame is represented by subchannels and symbols in a time domain and a frequency domain.
Referring to FIG. 1, a downlink frame includes a preamble field 101, DL-MAP fields 103 and 105, an MBS-MAP message field 109, and a plurality of MBS data burst fields, i.e., an MBS data burst 1 field 113, an MBS data burst 2 field 115, and an MBS data burst 3 field 117. Further, the DL-MAP field 103 includes an MBS_MAP_Information Element (MBS_MAP_IE) field 107, and the MBS-MAP message field 109 includes an MBS_Data_Information Element (MBS_Data_IE) field 111.
The preamble field 101 transmits a synchronization signal, i.e., a preamble sequence, for synchronization acquisition between a transmitter and a receiver. The DL-MAP fields 103 and 105, fields for transmitting DL-MAP information, include the MBS_MAP_IE field 107 to provide MBS, and an MBS_MAP_IE included in the MBS_MAP_IE field 107 provides information for decoding the MBS-MAP message field 109. A format of the MBS_MAP_IE included in the MBS_MAP_IE field 107 is shown in Table 1 below.
TABLE 1SyntaxSize (bits)NotesMBS_MAP_IE( ) {Extended DIUC4MBS_MAP=0x0ALength4MBS Zone Identifier7MBS Zone identifier corresponds to the identifierprovided by the BS at connection initiationMacro diversity enhanced10=Non Macro diversity enhanced zone1=Macro diversity enhanced zoneIf(Macro diversity enhanced=1) {Permutation20b00=PUSC permutation0b01=FUSC permutation0b10=Optional FUSC permutation0b11=Adjacent subcarrier permutationIDcell6}OFDMA symbol offset7OFDMA symbol offset with respect to start of theMBS regionDIUC change indication1Used to indicate DIUC change is includedIf(DIUC change indication=1) {  Reserved1  Boosting3  DIUC4  No. subchannels6  No. OFDMA symbols2 Repetition coding indication20b00=No repetition coding0b01=repetition coding of 2 used0b10=repetition coding of 4 used0b11=repetition coding of 6 used } else {  DIUC4  CID12 12 LSB of CID OFDMA symbol offset8The offset of the OFDMA symbol in which theburst starts, measured in OFDMA symbols frombeginning of the downlink frame in which the DL-MAP is transmitted.  Subchannel offset6The lowest index OFDMA subchannel used forcarrying the burst, starting from subchannel 0.  Boosting3  SLC_3_Indication1Used to notify sleep mode class 3 is used for singleBS MBS service  No. OFDMA symbols6  No. subchannels6  Repetition coding indication20b00=No repetition coding0b01=Repetition coding of 2 used0b10=Repetition coding of 4 used0b11=Repetition coding of 6 used If(SLC_3_Indication=0) {  Next MBS frame offset8The Next MBS frame offset value is lower 8bits ofthe frame number in which the BS shall transmit thenext MBS frame.  Next MBS OFDMA symbol8The offset of the OFDMA symbol in which the nextoffsetMBS zone starts, measured in OFDMA symbolsfrom the beginning of the downlink frame in whichthe MBS-MAP is transmitted.  } } If!(byte boundary) {  Padding nibbleVariablePadding to reach byte boundary }}
Table 1 shows Information Elements (IEs) of the MBS_MAP_IE included in the MBS_MAP_IE field 107. In Table 1, ‘Extended Downlink Interval Usage Code (Extended DIUC)’ indicates that the MBS_MAP_IE includes MBS-MAP information, and is set to have a value of ‘0×0A’. ‘MBS Zone Identifier’ indicates an identifier of the MBS field, ‘Macro Diversity Enhanced’ indicates whether macro diversity is applied to the MBS field, and ‘Permutation’ and ‘IDcell’ indicate information necessary when the macro diversity is applied to the MBS zone. Herein, the MBS field includes the MBS-MAP message field 109 having the MBS_Data_IE field 111, and a plurality of MBS data burst fields 113, 115 and 117.
In addition, ‘OFDMA symbol offset’ indicates a start offset of an MBS-MAP message in the MBS field, ‘DIUC change indication’ indicates a change in DIUC to be used for receiving the MBS-MAP message, and ‘No. Subchannels’ indicates the number of allocated subchannels. Further, ‘No. OFDMA Symbols’ indicates the number of allocated OFDMA symbols, and ‘Repetition coding indication’ indicates coding information to be used for decoding the MBS-MAP message. The IEs not mentioned in Table 1 are not directly related to the present invention, so a detailed description thereof will be omitted herein.
As shown in Table 1, the MBS_MAP_IE field 107 includes information on the MBS-MAP message field 109, and receivers receive the MBS-MAP message transmitted with the MBS-MAP message field 109 through the MBS_MAP_IE. With reference to Table 2, a detailed description will now be made of the MBS-MAP message. Table 2 below shows a format of the MBS-MAP message.
TABLE 2SyntaxSize (bits)NotesMBS-MAP Message format ( ) {  MAC Generic Header48 6bytes  Management message type=624  Frame number4The frame number is identical to the frame number inthe DL-MAP MBS_DIUC_Change_Count8 # MBS_DATA_IE4Number of included MBS_DATA_IE For(i=0;i<n; i++) {N= #MBS_DATA_IE   MBS_DATA_IEVariable  } #MBS_DATA_Time_Diversity_IE4Number of includedMBS_DATA_Time_Diversity_IE  For(i=0;i<m; i++) {m= #MBS_DATA_Time_Diversity_IEMBS_DATA_Time_Diversity_IEVariable  }  If(!byte boundary) {  Padding nibble8 }  TLV encoding element}
Table 2 shows a format of the MBS-MAP message transmitted through the MBS-MAP message field 109. The MBS-MAP message includes a 6-byte or 48-bit Medium Access Control (MAC) Generic Header, and a plurality of IEs. Of the IEs, ‘Management Message Type’ indicates a type of a management message, ‘Frame number’ indicates the same frame number as a frame number of the DL-MAP, and ‘MBS DIUC Change Count’ indicates whether the MBS data burst profile is identical to a previous MBS data burst profile.
If a value of the ‘MBS DIUC Change Count’ is changed, the receiver that received the MBS-MAP message should receive downlink burst profile information included as Time/Length/Value (TLV) information of the MBS-MAP message. However, if the downlink burst profile information is not included in the MBS-MAP message, the receiver receives the downlink burst profile information through a next Downlink Channel Descriptor (DCD) message. In addition, ‘MBS_Data_IE’ and ‘MBS_Data_Time_Diversity_Information Element’ (MBS_Data_Time_Diversity_IE) indicate field information of MBS data bursts that the receiver will receive. The ‘MBS_Data_Time_Diversity_IE’ includes information on MBS data bursts allocated when there is only the MBS burst data for a receiver supporting a Hybrid Automatic Repeat reQuest (HARQ) scheme. The IEs not mentioned in Table 2 are not directly related to the present invention, so a detailed description thereof will be omitted herein.
With reference to Table 3, a description will now be made of the MBS_Data_IE including information on the MBS data burst fields 113, 115 and 117 over which MBS data is transmitted.
TABLE 3SyntaxSize (bits)NotesMBS_DATA_IE {MBS_MAP_Type=04MBS_DATA_IENext MBS MAP change indication1This indicates whether the size of MBS MAPmessage of next MBS frame for these multicastCIDs included this IE will be different from the sizeof this MBS MAP message.No. of Multicast CID3For(i=0;i<No. of Multicast CIDs;i++) { Multicast CID1212 LSBs of CID for multicast}MBS DIUC4OFDMA symbol offset8OFDMA symbol offset with respect to start of theMBS portionSubchannel offset6OFDMA subchannel offset with respect to start ofthe MBS portionBoosting3No. OFDMA symbols7The size of MBS dataNo. subchannels6 Repetition coding indication20b00=No repetition coding0b01=Repetition coding of 2 used0b10=Repetition coding of 4 used0b11=Repetition coding of 6 usedNext MBS frame offset8The Next MBS frame offset value is lower 8 bits ofthe frame number in which the BS shall transmit thenext MBS frame.Next MBS OFDMA symbol offset8The offset of the OFDMA symbol in which the nextMBS portion starts, measured in OFDMA symbolsfrom beginning of the downlink frame in which theMBS-MAP is transmitted.If(Next MBS MAP changeindication=1) { Next MBS No. OFDMA symbols2It is to indicate the size of MBS_MAP message inNext MBS portion where the BS shall transmit thenext MBS frame for multicast CIDs in this IE. Next MBS No. OFDMA symbols6It is to indicate the size of MBS_MAP message inNext MBS portion where the BS shall transmit thenext MBS frame for multicast CIDs in this IE. }}
Table 3 shows IEs of the MBS_Data_IE transmitted through the MBS_Data_IE field 111. In Table 3, ‘MBS_MAP_Type’ indicates that the IEs of Table 3 are MBS_Data_IE, and ‘Next MBS MAP change indication’ indicates a change in size of an MBS-MAP message that will come in the next MBS frame, wherein the MBS frame means the frame that includes information of the MBS data or the data burst of the MBS. In addition, ‘Multicast Connection Identifier (CID)’ indicates multicast identifier information mapped to the MBS_Data_IE, ‘OFDMA Symbol Offset’ and ‘Subchannel Offset’ indicate start offsets of the MBS data burst fields 113, 115 and 117, and ‘No. Subchannels’ indicates the number of subchannels of the MBS data burst fields 113, 115 and 117 allocated to the MBS frame. Further, ‘No. OFDMA Symbols’ indicates the number of OFDMA symbols of the allocated MBS data burst fields 113, 115 and 117, and ‘Repetition coding indication’ indicates the number of repetitions (or iterations) needed for decoding the MBS data transmitted through the MBS data burst fields 113, 115 and 117.
In addition, ‘Next MBS frame offset’ indicates an offset of the next MBS frame, and ‘Next MBS OFDMA symbol offset’ indicates an offset of a downlink frame OFDMA symbol for receiving the next MBS-MAP message. Herein, if the ‘Next MBS MAP change indication’ is set to ‘1’, it means that the ‘Next MBS OFDMA symbol offset’ includes ‘Next MBS No. OFDMA symbols’ indicating a size of an MBS-MAP message that will come in the next MBS frame, and ‘Next MBS No. OFDMA subchannels’. After receiving the ‘Next MBS frame offset’ and the ‘Next MBS OFDMA symbol offset’, the receiver can obtain the MBS service information without receiving the MBS_MAP_IE of the DL-MAP. The IEs not mentioned in Table 3 are not directly related to the present invention, so a detailed description thereof will be omitted herein.
The foregoing MBS-MAP message serves as a MAC control message including information so that the receiver can decode the MBS data burst fields and the corresponding MBS data in MBS data transmitted through the fields. As a result, the MBS-MAP message shown in Table 2 provides information on the MBS data burst fields to the receivers, along with 48-bit MAC Generic Header, as described above. If the amount of information on the MBS data burst fields in which the MBS-MAP message is to be included is large, the MBS-MAP message may not include information on many MBS data burst fields that should be included in one MBS frame, because of the 48-bit MAC Generic Header. Accordingly, the MBS-MAP message is not fully transmitted in one MBS frame, and is transmitted in the next MBS frame, along with the MAC Generic Header.
As the MBS-MAP message is transmitted over two MBS frames together with the MAC Generic Header, the MAC Generic Header becomes an overhead. In addition, the transmitter transmits the MBS-MAP message over two MBS frames due to the 48-bit MAC Generic Header even for the information on the MBS data burst fields that can be transmitted in one MBS frame, thereby causing a waste of frequency bands. In order to prevent the waste of the frequency bands, it is also possible to allocate information on some of the MBS data burst fields to the current MBS frame before transmission, and transmit information on the other MBS data burst fields in the next MBS frame. In this case, there is a need for a scheme for additionally transmitting information indicating to which MBS frame the information on the MBS data burst fields included in the MBS-MAP message transmitted in the current MBS frame is allocated before being transmitted.
FIG. 2 is a diagram schematically illustrating a structure of an MBS frame in a general communication system providing MBS. In FIG. 2, an MBS-MAP message and information on MBS data burst fields included in the MBS-MAP message are transmitted over two frames of a particular frame n and the next frame (n+1). For convenience, FIG. 2 illustrates only the MBS field in the downlink MBS frame of FIG. 1.
Referring to FIG. 2, an MBS frame n 200 includes an MBS-MAP message field 201, and a plurality of MBS data burst fields that include an MBS data burst 1 field 211, an MBS data burst 2 field 213 and an MBS data burst 3 field 215. The MBS-MAP message field 201 includes a plurality of an MBS_Data_IE fields 203, 205, 207 and 209 each including MBS data burst field information. In addition, an MBS frame (n+1) 250, the next frame of the MBS frame n 200, includes an MBS-MAP message field 251, and a plurality of MBS data burst fields that include an MBS data burst 4 field 255 and an MBS data burst 5 field 257. The MBS-MAP message field 251 includes an MBS_Data_IE 253 including the MBS data burst field information. The MBS_Data_IEs transmitted through the MBS_Data_IE fields 203, 205, 207 and 209 included in the MBS-MAP message field 201 of the MBS frame n 200 include information on the MBS data burst fields 211, 213, 215 and 255. In addition, the MBS_Data_IE transmitted through the MBS_Data_IE field 253 included in the MBS-MAP message field 251 of the MBS frame (n+1) 250 includes information on the MBS data burst fields 257.
Because the MBS data burst fields 211, 213, 215 and 255 mapped to the MBS_Data_IE transmitted through the MBS_Data_IE fields 203, 205, 207 and 209 included in the MBS-MAP message field 201 of the MBS frame n 200 cannot be wholly allocated to one MBS frame, i.e., the MBS frame n 200, the receiver cannot fully receive the MBS data transmitted through the MBS data burst fields 211, 213, 215 and 255. Accordingly, the MBS data burst 1 field 211, the MBS data burst 2 field 213 and the MBS data burst 3 field 215 among the MBS data burst fields 211, 213, 215 and 255 are allocated to the MBS frame n 200, so that the receiver receives MBS data transmitted through the MBS data burst 1 field 211, the MBS data burst 2 field 213 and the MBS data burst 3 field 215 in the MBS frame n 200. In addition, the MBS data burst 4 field 255 among the MBS data burst fields 211, 213, 215 and 255 is allocated to the MBS frame (n+1) 250, so that the receiver receives MBS data transmitted through the MBS data burst 4 field 255 in the MBS frame (n+1) 250.
At this moment, the receiver cannot determine whether the transmitter has allocated the MBS data bursts 211, 213, 215 and 255 mapped to the MBS-MAP message field 201 of the MBS frame n 200 in the current MBS frame, i.e., the MBS frame n 200, or in the next MBS frame, i.e., the MBS frame (n+1) 250. Therefore, upon receiving the MBS frame n 200, the receiver decodes the MBS data of the MBS data burst 1 field 211, MBS data of the MBS data burst 2 field 213, and MBS data of the MBS data burst 3 field 215 received in the MBS frame n 200, using the MBS_Data_IE included in the MBS_Data_IE fields 203, 205 and 207 of the MBS-MAP message field 201. In addition, upon receiving the next MBS frame, i.e., the MBS frame (n+1) 250, the receiver decodes the MBS data of the MBS data burst 5 field 257 received in the MBS frame (n+1) 250 using the MBS_Data_IE included in the MBS_Data_IE field 253 of the MBS-MAP message field 251.
FIG. 2 illustrates operations 221, 223, 255 and 271 of decoding the MBS data transmitted through the MBS data burst fields 211, 213, 215 and 257, using the MBS_Data_IE in each frame. As described with reference to FIG. 2, in the MBS frame n 200, information on the MBS data burst fields included in the MBS-MAP message field 201 is information on the MBS data burst 1 field 211, the MBS data burst 2 field 213, the MBS data burst 3 field 215 and the MBS data burst 4 field 255. Although the information on the MBS data burst fields 211, 213, 215 and 255 is allocated to the MBS frame n 200 in this manner, the MBS data burst 4 field 255 is actually allocated to the MBS frame (n+1) 250.
However, the receiver receiving the MBS frame n 200 cannot determine that the transmitter has allocated the MBS data burst fields 211, 213, 215 and 255 as described above, using the MBS-MAP message and the MBS_Data_IE having the structures of Table 2 and Table 3, transmitted through the MBS-MAP message field 201 and the MBS_Data_IE fields 203, 205, 207 and 209 of the MBS frame n 200. Therefore, upon receiving the MBS frame n 200, i.e., the current MBS frame, the receiver performs an operation 227 of decoding the MBS data transmitted through the MBS data burst 4 field 255, considering that the MBS data burst 4 field 255 is allocated to the current MBS frame. However, because the MBS data burst 4 field 255 is not allocated to the MBS frame n 200, an error may occur in the receiver.
In addition, the receiver, receiving the MBS-MAP message with the MBS_Data_IE in a particular MBS frame, may not decode the MBS data transmitted through the MBS data burst fields mapped to the MBS_Data_IE in the particular MBS frame in a real time. That is, even though the transmitter has transmitted the MBS data through the MBS_Data_IE and the MBS data burst fields including allocation and decoding information of the MBS data burst fields in the particular MBS frame, the receiver may fail to decode the MBS data transmitted through the MBS data burst fields due to its processing delay.
Therefore, because the MBS data burst fields individually mapped to the MBS data burst fields included in the MBS_Data_IE of the MBS-MAP message should be allocated to the same MBS frame as the MBS-MAP message field through which the MBS-MAP message is transmitted, there is a need for a scheme for reducing a size of the MBS-MAP message. In addition, there is a demand for a scheme for reducing a processing error which may occur when the receiver recognizes an MBS frame to which the MBS data burst fields are allocated, and decodes the MBS data transmitted through the MBS data burst fields. Further, there is a need for a scheme in which the transmitter provides the receiver with information used for previously decoding the MBS data before a transmission time of the MBS data through the MBS data burst fields, and an allocation time of the MBS data burst fields through which the MBS data is transmitted, i.e., a transmission time of the MBS data, thereby preventing the processing delay of the receiver.